This, I think, is the modern edition that had been suggested to me, but at 28 pages it seems to be about him rather than a full re-issue of the original memoirs. Either that, or it is extracts, since the original is listed elsewhere as having 164 pages.
http://www.amazon.co.uk/Thomas-Jackson-Walsall-Soldier-Napoleonic/dp/0946652325

So unless anyone has any leads re. an online version of the original, it looks like I'm off to the British Library.